The invention relates to a method for supplying combustion air to a combustion chamber. Further, the invention relates to suitable arrangements in a combustion chamber as well as a special use of oxygen-containing exhaust from a gas turbine or another engine fuel combusting unit/equipment/apparatus.
More specifically, the invention relates to a method associated with the supply of oxygen-containing combustion air to a first engine fuel combusting unit, e.g. a combustion chamber. The arrangements involving a combustion chamber according to the invention is of the kind including a combustion chamber which may be assigned to a refining unit for gases, a so-called reformer which, possibly together with one or more further reformers, may be included in a process plant, and/or one or more other units which might have a need for supplied heat energy from one or more combustion chambers, for instance for heat treatment of gases within said unit(s), which reformer or each reformer, respectively, may comprise a reactor chamber assigned a combustion chamber, possibly one combustion chamber each, adapted to be supplied with gas or liquid fuel and oxygen-containing combustion air for the burning thereof, and where the heat energy produced in the combustion chamber is supplied to e.g. said reactor chamber, in which for instance a gas treatment is carried out such as a heat treatment of methane which, in treated condition, may be taken out in the form of synthesis gas for e.g. methanol production. The use of oxygen-containing exhaust from e.g. a gas turbine as combustion air for e.g. a combustion chamber, is more specifically defined.
The arrangements and devices in accordance with the invention may for instance be used in a combustion chamber, which may be assigned a so called xe2x80x9creformerxe2x80x9d which may on its side be incorporated into a process plant, and which reformer comprises a reactor chamber for the treatment of gases. The combustion chamber, as well known, is supplied with gas or liquid engine fuel and combustion air. In the reactor chamber, for example, methane-containing gas may be treated for the achievement of a refined methane gas upon supplied heat from the combustion of engine fuel in the combustion chamber during combustion air supply. The process plant comprises at least one gas turbine which may be adapted to operate a generator for the generation of electrical current, e.g. for use within the process plant.
During the development of the present invention, importance has been especially attached to the reduction of energy consumption and to exhaust discharge from the process plant, i.e. gas effluents such as CO, CO2, NOx and VOx to the atmosphere and/or into water.
The invention is particularly, yet not exclusively, aimed at providing an offshore production plant, e.g. a methanol factory built up on an offshore installation, and which does not contaminate the surroundings any more than the very best plants on land and wherein, moreover, as previously mentioned, large energy savings and exhaust discharge reductions are achieved. The invention applies also in relation to plants ashore. In offshore production the necessary energy must be provided in situ through the combustion of fossil fuel in lieu of electrical power, which often is produced ashore by means of waterpower.
Methane, CH4, is as known the most important constituent in natural gas and appears i.e. as gas exiting from the crust of the earth. So called methane towers are known in the form of distillation towers for evaporating methane.
Upon the adaptation of, for instance, a methanol factory at an offshore production plant, substantial energy supply in the form of electrical current and heated air is required. Total need of electricity for installations of this kind could vary from 10 to 50 MW, while the need for hot air having a high temperature, e.g. 650xc2x0 C., could vary from 50 to about 200 kgs/second.
Conventionally, these types of energy are provided by means of separate gas turbine operated generators for the generation of electrical current and combustion chambers for the combustion of gas or liquid fuel during the supply of combustion air, and production of heated air having the required temperature (650xc2x0 C.), said combustion chambers being incorporated in suitable reformers which, likewise, comprise a reactor chamber which is fed with gas for treatment, the reformers being included in a process plant.
In the combustion chamber, the necessary amounts of air must be heated from ambient air temperature to the desired exhaust temperature. This means that the combustion chamber must be supplied with a substantial amount of fuel. Simultaneously, the combustion air must be allotted the necessary energy to cause flowing, such as from fans or the like, for forced supply to the combustion chamber of the reformer. This energy is typically produced by either a gas turbine or an internal combustion engine.
The above scheme results in a low total energy efficiency, and simultaneously, in offshore plants suffers from larger exhaust discharges than corresponding industry ashore.
The device according to the invention enables an increase of the total efficiency of the reformer (or each reformer, respectively, in case the process plant comprises more than one) by reducing the need for energy for a reformer as discussed above. The invention simultaneously effects a reduction in the discharge amount of exhaust from the same reformer""s combustion chamber through the reduction of the amount of fuel supplied to the combustion chamber/chambers.
To this end, the invention may distinguish itself through the features of oxygen containing exhaust gas from a second fuel-burning unit, for example, a gas turbine, is led to a first fuel-burning unit, said exhaust gas preferably leaving said second fuel-burning unit""s exhaust gas outlet at an overpressure.
According to the invention, exhaust gas from the gas turbine may be supplied as combustion air to the reformer""s combustion chamber. As previously known, the gas turbine operates an electrical generator or another mechanical equipment.
As a rule, the oxygen-content in the exhaust gases from a gas turbine will be satisfactory in order to secure good combusting in the combustion chamber. However, it is within the scope of this invention possibly to supply a small amount of combustion air rich on oxygen in addition to a larger amount of gas turbine exhaust gas.
The exhaust gases from the gas turbines are preferably blown with an overpressure of up to 0.5 bar into the combustion chambers, in which gas or liquid engine fuel supplied thereto burns in order to bring the final temperature up to the necessary value of 650xc2x0 C.
A a result electrically operated fans for forced supply of cold combustion air to the combustion chamber normally could be left out, totally resulting in quite substantial energy savings and reduced amount of exhaust gas.
Combustion gas in the form of hot turbine exhaust gas involves the great advantage over cold combustion air that the former is preheated to a substantial degree. Thus, a preheating up to a temperature of about 450xc2x0 C. can be achieved, dependent on the load on the gas turbine. This entails an energy saving in relation to prior art technique where a significant amount of energy is consumed in order to heat combustion air supplied to the combustion chamber at ambient temperature, up to said 650xc2x0 C. from e.g. 15xc2x0 C. in relation to up to said 650xc2x0 C. from gas turbine exhaust gas temperature of about 450xc2x0 C. This very substantial preheating of the combustion gas received by the combustion chamber also allows energy savings, which here manifest themselves in a reduction of propellant gas amount supplied per time unit to the combustion chamber which becomes significantly less power consuming as a result of the heat energy brought into the combustion chamber with the combustion gas/air.
Significant environmental improvements are achieved through temperature reduction by the combustion in the reformer, and by leaving out a combustion air fan. Reduction of the amount of fuel supplied to the combustion chamber per time unit has also a positive influence on the exhaust gas discharges, particularly CO2 in the surroundings in relation to conventional installations, both plants ashore and plants offshore.